This invention relates generally to the positioning of a tubular duct in a conduit and is particularly directed to apparatus for engaging the inner surface of a duct to facilitate drawing it lengthwise through and positioning it within a conduit.
Electrical conductors located within a building structure or buried underground are generally positioned within a circular duct. Frequently many of these ducts are co-located within a single conduit. The ducts serve to isolate the electrical cables from one another in not only preventing the cables from contacting and rubbing against each other but also reducing the likelihood of electrical interference between adjacently positioned cables. Isolating cables positioned within a single conduit from one another is particularly important in the case of fiber optic cables which are being used on an ever increasing basis particularly in the field of telecommunications.
In general, a device is attached to one end of a duct to permit the duct to be pulled through the conduit for positioning the duct therein. Prior art duct pulling devices have suffered from various shortcomings. For example, currently available duct pulling devices provide only a limited engaging force with the duct being pulled and thus are generally limited to pulling relatively short lengths of duct. This, of course, increases the cost of laying the conduit because more frequent interruptions for pulling the duct and coupling adjacent lengths of conduit are required. In addition, prior art duct pulling devices have generally been larger in diameter than the duct being pulled and thus restrict the number of ducts which can be positioned within a given conduit to the cross sectional dimensions of the duct pulling device. This also increases the cost of installing electrical and communications lines. In addition, prior art duct pulling devices are of limited use with corrugated ducts which are finding increasing usage because of their flexibility. This is due to the reduced lateral engaging surface area of corrugated ducts which limits the pulling force of prior art pulling devices when used with this type of duct. Finally, prior art duct pulling devices are generally limited to use with ducts having a given cross sectional dimension.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing a duct pulling tool capable of firmly engaging tubular ducts having a wide range of cross sectional dimensions for facilitating the positioning of the duct within and along the length of a conduit. The duct pulling tool of the present invention has an outer diameter less than that of the duct being pulled, is capable of securely engaging corrugated ducts, and permits a plurality of ducts to be pulled through a single conduit simultaneously.